1. Field of the Disclosure
The present invention relates to optical glasses, in particular to special short flint glasses (German: Kurzflintsondergläser (KZFS)) and optical elements and components, which comprise these glasses, as well as use thereof and a method for production of such optical glasses.
2. Description of the Related Art
Correction of chromatic aberration is an important issue in optical systems of high quality already from the design of the system on. Glasses with pronounced short-flint properties are indispensable for an excellent correction of chromatic aberrations. Such glasses are glasses that have a relative partial dispersion that deviates significantly from the normal line so that the glasses are particularly suitable for correction of chromatic abberations.
Common optical glasses and their optical applications as object lenses, for digital projection (for example objectives, binoculars, microscopes, projectors, mobile phone cameras, mobile drive) often do not fulfill the properties of a negative anomalous partial dispersion and/or the requirements of a high chemical resistance.
Moreover, provision of optical glasses is desirable that have a content of lead and arsenic as low as possible and that are preferably even free of lead and arsenic because these components have been classified as pollutive components. Furthermore, the economic efficiency of a glass is more and more getting into the focus of attention of glass producers and producers of optical instruments and products. Therefore, it is also desirable that raw materials, which are on a high price level due to globally and also locally limited reserves, as for example Ta raw materials and GeO2, are as much as possible reduced as component in a glass or preferably even avoided. Thereby it would also be ensured that such a glass can be provided in the future. Furthermore, glasses with increased chemical resistance are continuously getting more and more important in products of high quality.
In particular, only a part of the chromatic aberration can be eliminated in lens systems by combination of glasses having differing Abbe numbers. The remaining chromatic aberration, the so called secondary spectrum, is reduced by applying glasses having strongly deviating partial dispersions. The latter means the combination of glasses which have a negatively deviating partial dispersion with glasses which have a positively deviating partial dispersion in a lens system.
Often this optical property of negatively deviating anomalous partial dispersion is caused by use of PbO and/or Ta2O5, which should be avoided or reduced as much as possible for the above-mentioned ecological and economical reasons.
However, PbO and Ta2O5 are components, which are able to cause a particularly small anomalous partial dispersion. A reproduction of the desired optical and glass-technological properties influenced by PbO and/or Ta2O5 can normally not be achieved by a simple replacement by one or more components. Instead, new developments or far-reaching changes in the glass composition are necessary.
Known lead-free and/or tantalum-free glasses of the desired optical position are normally based on use of very high amounts of alkali oxides and/or B2O3 in a silicate matrix, which usually results in a glass with low resistance against acids and/or alkaline solutions. Moreover, known glasses, which have a similar optical position as the one achieved according to the present invention or which have a comparable chemical composition, have significant disadvantages, in particular in direct comparison with the glasses of the present invention:
The combination of components of the glasses described in document DE 10 2007 025 601 A1 does not result in a glass, which combines all optical and simultaneously physical properties. Moreover, the glass is described as a “short” glass having the feature that T(T(∥) at 107,6−T( ) at 1013) is at most 150 K. The glasses of the invention have T>150 K due to the lack of ZnO and the obligatory presence of the oxide of calcium in the document. Furthermore, the content of B2O3 is too low in the glass.
Document DE 102 25 366 discloses glasses having higher contents of SiO2 and lower contents of B2O3, which moreover obligatorily contain ZrO2 in an amount of more than 10 to 20% by weight. This combination leads to a glass having Tg of significantly higher than 560° C. Moreover, the melting temperatures are increased, which is economically inefficient. Furthermore, it is not readily possible that such a glass is further processed by re-pressing. Glasses disclosed in document WO 01/72650 A1 obligatorily contain Nb2O5 of from 20 to 50% by weight. This component is useful for increasing the refractive index and reducing the Abbe number. However, with these amounts an advantageous optical refractive index position cannot be achieved. Furthermore, Nb2O5 is a redox-sensitive component and leads to glasses having impaired transmittance.
It is an object of the invention that the above-described disadvantages are overcome.